Vapor deposition temperature control apparatus and method

ABSTRACT

Coating temperature during vapor deposition of a ceramic coating on a substrate in a coating box or enclosure is maintained by means of a heat release cover or lid on the coating enclosure and movable in response to temperature in the coating enclosure exceeding a predetermined value so as to release excess heat from the enclosure to maintain coating temperature within an appropriate range.

This is a division of Ser. No. 09/201,648 now U.S. Pat. No. 6,319,569filed Nov. 30, 1998.

FIELD OF THE INVENTION

The present invention relates to vapor deposition and, moreparticularly, to physical vapor deposition of ceramic materials to formcoatings on substrates.

BACKGROUND OF THE INVENTION

Ceramic coatings are applied to gas turbine engine hardware, such asturbine blades and vanes, to provide thermal protection against the hightemperatures of the turbine engine. For example, so called thermalbarrier coatings are applied to gas turbine engine blade and vanecomponents by first depositing a bondcoat on the component followed bydepositing a ceramic layer on the bondcoat by electron beam physicalvapor deposition. In the electron beam physical vapor deposition of theceramic layer, a source of the ceramic material, such as yttriastabilized zirconia, is heated by impinging an electron beam thereon toevaporate the ceramic material for deposition on the components, whichare positioned in the ceramic vapor cloud to this end.

The electron beam physical vapor deposition of the ceramic layer on theturbine components is conducted in a stainless steel or other coatingbox or enclosure, which may be water cooled. It has been discovered byapplicants that during the course of coating with the evaporated ceramicmaterial, the ceramic coating material inadvertently collects on theinside walls of the relatively cool coating box or enclosure in additionto depositing on the components to be coated. The collected ceramicmaterial has been found to act as thermal insulation on the insideenclosure walls to an extent that excess heat can build up in thecoating box or enclosure exceeding the preselected desired coatingtemperature for the particular components to be coated, resulting indefective or unacceptable coated components.

It is an object of the present invention to provide method and apparatusthat overcome the aforementioned problem and provide control of coatingtemperature during vapor deposition in a coating box or enclosure.

SUMMARY OF THE INVENTION

The present invention provides control of coating temperature duringvapor deposition in a coating box or enclosure by means of a heatrelease lid or cover on the coating enclosure and movable in response totemperature in the coating enclosure so as to release excess heat from aheat vent opening of the enclosure to maintain coating temperaturewithin an appropriate range.

In an illustrative embodiment of the present invention, a water cooledor non-cooled metal (e.g. water cooled copper or non-cooled stainlesssteel) coating enclosure includes a heat release cover movable relativeto a heat vent opening of the enclosure. An actuator is connected to theheat release cover for raising away from the opening to discharge orvent excess heat in response to temperature inside the enclosureexceeding a predetermined value to maintain coating temperature withinan appropriate range. Temperature in the coating enclosure is sensed bya thermocouple or other temperature sensing device and provides atemperature feedback signal to an automatic actuator or to a temperaturegage monitored by a coating operator who raises or lowers the lid inresponse to sensed temperature in the coating enclosure.

The above objects and advantages of the present invention will becomemore readily apparent from the following detailed description taken withthe following drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation of a vapor deposition apparatus in accordancewith an embodiment of the invention.

FIG. 2 is a partial side elevation of the same apparatus taken normal toFIG. 1 with the coating enclosure open on a side to reveal substratesand substrate manipulator.

FIG. 3 is an enlarged partial sectioned view of the lid lift actuatorassembly.

FIG. 4 is partial elevational view of the baffles on the enclosure sidewalls and the wall of the heat release cover.

DESCRIPTION OF THE INVENTION

In an embodiment of the present invention offered for purposes ofillustration and not limitation, the substrate coating temperatureduring electron beam physical vapor deposition of a ceramic material ona substrate is maintained within appropriate preselected range toproduce an acceptable coated substrate. For example only, thetemperature of a superalloy substrate, such as a gas turbine engineblade or vane, having a bondcoat is maintained within appropriatepreselected coating temperature range of, for example only, 1700 to 2000degrees F. to achieve columnar ceramic coating structure that ischaracteristic of an acceptable coated superalloy substrate for servicein a gas turbine engine during electron beam physical vapor depositionof a ceramic material thereon. The ceramic material typically cancomprise yttria stabilized zirconia, or other suitable ceramic material,for deposition onto a metallic or intermetallic bondcoat comprising analuminide diffusion layer, MCrAlY layer where M is Ni, Co, and/or Fe, orother suitable bondcoat, applied on the substrate as described, forexample, in U.S. Pat. No. 5,716,720, the teachings of which areincorporated herein by reference to this end.

Referring to FIGS. 1-4, electron beam vapor deposition coating apparatusin accordance with an illustrative embodiment of the invention isillustrated as comprising a water cooled copper or stainless steelnon-cooled coating box or enclosure 10 supported by various supportmembers 13 inside a vacuum chamber C. Typically, multiple substrates S(two shown for convenience) to be coated are held in the enclosure 10 ingrips or fixtures 12 of manipulator 18 shown schematically in FIG. 2 andforming no part of the invention. As mentioned above, the substrates Scan comprise gas turbine engine blades or vanes having a bondcoatthereon. The manipulator 18 typically rotates the blades or vanes abouttheir longitudinal axes during coating.

The coating enclosure 10 includes four side walls 10 a, a bottom wall 10b and a top wall 10 c, which can be water cooled copper walls ornon-cooled stainless steel walls. Bottom wall 10 b has a pair of ingothearths 14 disposed therein. The walls 10 a and top wall 10 c can bewater cooled by flexible cooling water supply and return lines 11 a, 11b connected to a source of cooling water (not shown), such as a closedcircuit chiller, and copper tubing (not shown) on the outside surfacesof the enclosure walls when a water cooled copper enclosure is employed.Electron beam guns 100 in the top wall are adapted to direct respectiveelectron beams to impinge on sources 15 of ceramic material, such as forexample yttria stabilized zirconia ingots, in a manner to evaporateceramic material from the sources 15 to form vapor clouds in which thesubstrates S are rotated by manipulator 18 for deposition of thevaporized ceramic material thereon as a coating.

The coating box or enclosure includes top wall 10 c having a heat ventopening 10 d therein which is closed off by a heat release cover 20 thatcomprises water cooled or non-cooled stainless steel copper plate. Theheat release cover 20 is sized to overlie the opening 10 d and a portionof the top wall 10 c of the enclosure so as to, in effect, close off theheat vent opening 10 d when the cover 20 resides on the top wall 10 c asshown in FIGS. 1-2. There is no seal on the cover 20 or the top wall. Inthe closed position shown, the cover 20 substantially prevents heat fromescaping from the coating enclosure 10 via the vent opening.

The cover 20 is lowered by an actuator assembly 30 mounted on posts 33to the closed position shown in solid lines to close off the heat ventopening or raised to the dashed line position to open the opening 10 dto vacuum chamber C to release or vent excess heat. The actuatorassembly includes electric actuator 32 located outside the vacuumchamber C atop an actuator housing 34 that is vacuum tight sealed (e.g.bolted with O-ring seals not shown) on the vacuum chamber C. Theactuator 32 may comprise an electric linear actuator available fromIndustrial Devices Corp. as model #ND355B4-MF1-FC2-BS-L with RPS-1accessories for lowering/raising the cover 20 relative to opening 10 d.

The actuator 32 includes a ball screw 32 a and rod 32 b with the rodconnected by a clevis pin 36 to lift rod 38 that extends through avacuum seal assembly 45 disposed on the top wall 34 a of the housing 34.Referring to FIG. 3, the top wall 34 a is mounted on the housing 34 withan O-ring seal 42 therebetween and the lift rod 38 extends throughvacuum seal assembly 45 that includes a rod guide housing 46 fastened tothe support plate by threaded bolts or fasteners 48 with an O-ring 50therebetween. Various sealing/bearing elements are disposed between therod guide housing 46 and the lift rod 38 such as Parker Poly-Pak seal 51available from Parker Hannifin Corporation, bronze spacer 52, seal guardwiper seal 53 and bronze housing 54 in FIG. 3.

The lift rod 38 is connected by a clevis pin 60 to a lift bracket 70inside the vacuum chamber C as shown in FIG. 3. The lift bracket, inturn, is connected to upwardly extending flanges 20 a of the cover 20 byconventional fasteners 72. In this manner, the heat release cover 20 canbe lowered/raised by the actuator assembly 30 relative to the heat ventopening 10 d.

The cover 20 can be water cooled via flexible cooling water supply andreturn lines 21 a, 21 b connected to a source of cooling water (notshown) such as closed circuit chiller and copper tubing 23 on theoutside surface of the cover 20.

The inside of the enclosure walls 10 a and the inside wall of the cover20 include baffle assemblies B for purposes of condensate collection andremoval. The baffle assemblies, FIG. 4, each comprise an innermoststainless steel wire cloth (8 mesh) sheet 80 and multiple stainlesssteel foil sheets 81 each comprising a heat shield supported on fastener(e.g. bolt) 82 retained by lock washer 83 and wire 85. The fastener 82is mounted on the enclosure inner walls 10 a and inner wall of the cover20 using the bolt head 82 a and nut 84.

During coating of the substrates S in the coating enclosure 10, arelative vacuum is maintained in vacuum chamber C and in the enclosure10. The cover 20 initially is positioned on the top wall 10 c of theenclosure to close off the heat vent opening 10 d as shown in solidlines in FIGS. 1-2. In continuous operation of the coating machine,vaporized ceramic build-up accumulates on the enclosure 10 and slows thetransfer of heat away from the enclosure. Consequently, the temperaturein the enclosure 10 rises with operation time. The temperature rise isdetected by thermocouple 110 located on the enclosure 10 or onmanipulator 18 and provides a signal indicative of excess heat and acorresponding substrate coating temperature outside the preselectedspecification range.

The actuator assembly 30 is actuated in response to the excesstemperature detected in the enclosure 10. In particular, the actuator 32is actuated to raise the cover 20 away from the top wall 10 d to openthe heat vent opening to the vacuum chamber C to release the excess heatand maintain the desired substrate coating temperature range in theenclosure 10. The cover 20 will remain raised above the opening 10 d aslong as necessary to maintain the substrate coating temperature inresponse to the sensed temperature in the enclosure 10. When appropriatesubstrate coating temperature returns within the specified range, thecover 20 can be lowered by the actuator assembly 30 fully back onto thetop wall 10 c or partially to any distance toward the top wall necessaryto maintain temperature specifications in the enclosure. The presentinvention thereby provides method and apparatus that for controllingsubstrate coating temperature during vapor deposition in a coating boxor enclosure in a manner that produces acceptable coated components.

Although the invention has been described in terms of specificembodiments thereof, it is not intended to be limited thereto but ratheronly to the extent set forth hereafter in the appended claims.

We claim:
 1. Vapor deposition coating apparatus comprising, an outervacuum chamber, a coating enclosure which is disposed in said outerchamber and in which a substrate to be coated is positioned, a heatrelease cover closing off a heat vent opening in said coating enclosure,and an actuator connected to said cover and responsive to temperature insaid coating enclosure to move said cover in a manner that said heatvent opening communicates an interior of said coating enclosure to saidouter vacuum chamber to release excess heat from said coating enclosureto said outer chamber and maintain substrate coating temperature in apreselected temperature range.
 2. The apparatus of claim 1 wherein saidheat vent opening is disposed in a top wall of said coating enclosureand said cover overlies said heat vent opening.
 3. The apparatus ofclaim 1 wherein said coating enclosure and said cover are water-cooledor non-cooled.
 4. The apparatus of claim 1 wherein said actuatorcomprises a ball screw having a rod connected to said cover.
 5. Theapparatus of claim 4 wherein said actuator includes a housing that isair tight sealed on the vacuum chamber in which said coating enclosureis positioned.
 6. The apparatus of claim 1 including a temperaturesensor for sensing temperature inside said coating enclosure duringcoating and providing a signal to said actuator.